Biotic resistance limits the invasiveness of the western flower thrips,Frankliniella occidentalis (Thysanoptera: Thripidae), in Florida

The spread of the western flower thrips, Frankliniella occidentalis (Pergande), has resulted in the world‐wide destabilization of established integrated pest management programs for many crops. It is hypothesized that frequent exposure to insecticides in intensive agriculture selected for resistant populations, which allowed invasive populations in the eastern USA to overcome biotic resistance from the native community of species. Research conducted in Florida to understand the role of biotic factors in limiting the abundance of the western flower thrips is reviewed. Orius spp. (Hemiptera: Anthocoridae) are effective predators that suppress populations of thrips on crop and non‐crop hosts in southern and northern Florida. Orius are more effective predators of the western flower thrips than the native flower thrips, F. tritici (Fitch) and F. bispinosa (Morgan). The native species are competitors of the western flower thrips. Excessive fertilization and the use of broad‐spectrum insecticides in crop fields further enhances populations of the western flower thrips. Interactions with native species clearly limit the abundance of western flower thrips in Florida, but populations are abundant in fertilized crop fields where application of insecticides excludes predators and competitor species.     

Plant traits mediate effects of predators across pepper (Capsicum annuum) varieties

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Intraspecific larval competition in two solitary parasitoids, Apoanagyrus (Epidinocarsis) lopezi and Leptomastix dactylopii

Analysis of total aromatic amino acid (free and bound) in some cucumber accessions selected previously for resistance to western flower thrips, Frankliniella occidentalis (Pergande) [Thysanoptera: Thripidae], indicated that low concentrations of these essential nutrients, relative to total leaf protein, were correlated with a reduction in damage by the insect. Further analysis of samples of four important horticultural crops (lettuce, tomato, pepper and cucumber) with unknown levels of resistance to thrips showed a significant genotypic variation in the concentrations of total aromatic amino acids relative to the total leaf protein. Accessions from each crop with low or high concentrations of aromatic amino acids in proteins were exposed to thrips larvae. Regression analysis showed a highly significant positive correlation between aromatic amino acid concentration in leaf protein and thrips damage, regardless of crop species. It is concluded that higher concentrations of aromatic amino acids in plant proteins are important for successful thrips development. These results provide plant breeders with a promising tool for indirect selection without using undesirable insect bioassays.     

Evaluation of efficacy of Neoseiulus cucumeris for control of western flower thrips in spring bedding crops

Western flower thrips, Frankliniella occidentalis (Pergande), is the principal insect pest of spring flower crops grown in the northeastern United States for use as bedding plants. Neoseiulus (=Amblyseius) cucumeris (Oudemans) is a predacious mite reared commercially that is recommended for control of western flower thrips in various vegetable and flower crops at a rate of ca 53 mites/m²/week. Efficacy on spring flower crops, however, is not well demonstrated, reports being either from other crops or extension demonstration trials. In two trials (each replicated), we compared suppression of western flower thrips in spring bedding plants provided by (1) N. cucumeris at the recommended rate, (2) spinosad (at the labeled rate), the most widely used thrips-control pesticide, and (3) both combined. Trial No. 1 was run in mixed bedding plants in commercial greenhouses and Trial No. 2 in impatiens monocultures in University greenhouses. We found that in commercial greenhouses, variation in species composition of crops and movement of plants during crop production made it difficult to detect any significant effects. In an impatiens monoculture (Trial No. 2), we found better evidence of partial suppression of thrips larvae and adults by treatments. Spinosad alone provided the best control, with mites alone usually providing control intermediate to that of spinosad alone and the untreated control. Control from spinosad plus mites was not significantly different from that of spinosad alone (all treatments evaluated as counts of thrips per plant, in flowers). In another University-based trial (Trial No. 3), we compared the commercially recommended rate of N. cucumeris (53 mites/m²/week) to a 3- to 4-fold higher rate (190 mites/m²/week) in impatiens monocultures. This trial was replicated twice in the fall of 2004 and once in spring of 2005 in Amherst, Massachusetts. We found that the higher release rate, while not resulting in statistically significantly more mites per plant (in flowers) than the standard rate, did suppress thrips larvae per plant (in flowers) by 50–75%, a higher level than that achieved by the recommended standard rate. No reductions, however, were found in counts of adult thrips, either as numbers per plant (in flowers) or as numbers caught per yellow sticky card, except for one replication in which thrips counts were lowered compared to controls by mites (at both release rates). We conclude that N. cucumeris, especially at the higher rate, provides partial control of western flower thrips in impatiens bedding plants, but that control from spinosad is better. Biological control of western flower thrips with this predator is not a complete thrips IPM program, but may be used together with spinosad or other materials to prevent development of pesticide resistance. This approach is most likely to be of value in crops grown as continuous relay plantings or a series of different, but thrips-susceptible, crop species.     

The spread of the western flower thrips Frankliniella occidentalis (Pergande)

Abstract 1 Since the late 1970s, the western flower thrips has spread from its original distribution in western North America to become a major worldwide crop pest. 2 A wide range of data sources have been used to map the original distribution in the U.S.A. and Canada, and the progress of the spread in the U.S.A., Canada, Europe, northern Africa and Australia. 3 The possible reasons for the start of the spread are discussed. The most likely reason is that intensive insecticide use in horticulture in the 1970s and 1980s selected an insecticide resistant strain or strains. These then established in glasshouses across North America and spread from there to Europe, Asia, Africa and Australia. 4 The international spread of the western flower thrips occurred predominantly by the movement of horticultural material, such as cuttings, seedlings and potted plants. Within Europe, an outward spread from the original outbreak in the Netherlands is discernible. The speed of spread was 229 ± 20 km/year. 5 The spread has not been restricted to glasshouses. The western flower thrips has established outdoors in areas with milder winters; for example, across the southern U.S.A., southern Europe and Australia. It also overwinters in some regions with colder winters. 6 Polyphagous phytophagous thrips have many factors predisposing them to become worldwide crop pests, particularly in glasshouses. Some other species that might spread in a similar way to the western flower thrips are listed.     

Decision-making tools for Frankliniella occidentalis management in strawberry: consideration of target markets

The western flower thrips (WFT), Frankliniella occidentalis Pergande (Thysanoptera: Thripidae), a cosmopolitan pest of many crops, is considered a major pest of low tunnel and greenhouse strawberries. The extent of damage to strawberry is unclear because different studies have produced contradictory results. Also, economic thresholds published for WFT in strawberry vary greatly, and most fail to incorporate economic factors. This study was aimed at developing a decision‐making tool for WFT management in strawberries in Israel. Toward this end, economic injury levels (EIL) and economic thresholds were calculated, based on target markets (export vs. domestic). Results indicate that serious infestation of ripe berries may cause a dull, rough appearance, and the fruit may be soft and have a reduced shelf life, rendering it unsuitable for export. Most fruit damage occurred at green and turning‐red stages of development. Two decision‐making tools were developed, one for winter, when WFT populations increase slowly but crop value is high (export market); and the second for spring, when the pest increases rapidly but crop value is low (local markets). Economic thresholds of 10 and 24 WFT/flower were calculated for winter and spring strawberries, respectively, based on direct thrips damage to fruit. This calculation does not take into account the recorded WFT damage to flowers, or its role in facilitating Botrytis cinerea fruit infection. Western flower thrips has proved only an occasional economic pest in Israeli strawberries, and no routine control measures are warranted. Furthermore, augmentative releases of Orius laevigatus or Neoseilus cucumeris against WFT are not justified in this system, because Orius colonizes strawberry fields spontaneously in high numbers when no broad spectrum insecticides are used.     

Genetic variation in chrysanthemum for resistance toFrankliniella occidentalis

In a choice-experiment, 42 chrysanthemum cultivars were screened for resistance toFrankliniella occidentalis (Pergande). Oviposition preference, two types of feeding damage and thrips numbers per flower were recorded as measures of resistance. A large genetic variation in thrips resistance was found among the cultivars screened. The amount of feeding damage was strongly determined by oviposition preference. Besides, a positive correlation was found between the oviposition preference in non-flowering chrysanthemums (number of eggs) and flowering chrysanthemums (number of thrips per flower). Thrips feeding on young, developing tissues, causes growth damage because affected cells are unable to expand and leaves become distorted. Thrips feeding on older, expanded leaves causes cells to become filled with air, resulting in ‘silver’ damage. The amounts of growth-and ‘silver’ damage were negatively correlated suggesting that thrips chose either young or older leaves to feed on. The order of resistance among cultivars did not change during the experiment. In order to get more insight in resistance mechanisms the influence of some plant- and flower characters on resistance was examined. The plant characters height, number of leaves, flower production and flower weight were all negatively correlated with resistance. It is suggested that tall chrysanthemum cultivars with many and large flowers may invest less in defence than smaller cultivars, and therefore are more damaged by thrips.     

Population genomic analyses reveal a history of range expansion and trait evolution across the native and invaded range of yellow starthistle (Centaurea solstitialis)

Identifying sources of genetic variation and reconstructing invasion routes for non‐native introduced species is central to understanding the circumstances under which they may evolve increased invasiveness. In this study, we used genome‐wide single nucleotide polymorphisms to study the colonization history of Centaurea solstitialis in its native range in Eurasia and invasions into the Americas. We leveraged this information to pinpoint key evolutionary shifts in plant size, a focal trait associated with invasiveness in this species. Our analyses revealed clear population genomic structure of potential source populations in Eurasia, including deep differentiation of a lineage found in the southern Apennine and Balkan Peninsulas and divergence among populations in Asia, eastern Europe and western Europe. We found strongest support for an evolutionary scenario in which western European populations were derived from an ancient admixture event between populations from eastern Europe and Asia, and subsequently served as the main genetic ‘bridgehead’ for introductions to the Americas. Introductions to California appear to be from a single source region, and multiple, independent introductions of divergent genotypes likely occurred into the Pacific Northwest. Plant size has evolved significantly at three points during range expansion, including a large size increase in the lineage responsible for the aggressive invasion of the California interior. These results reveal a long history of colonization, admixture and trait evolution in C. solstitialis, and suggest routes for improving evidence‐based management decisions for one of the most ecologically and economically damaging invasive species in the western United States.     

Can semiochemicals attract both western flower thrips and their anthocorid predators?

Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) (western flower thrips, WFT) is a key pest in a range of crops worldwide. Anthocorid species (Hemiptera) are important natural enemies of thrips. Several experiments were undertaken to determine whether a thrips lure, methyl isonicotinate (MI), affected the behaviour of WFT and anthocorids found in outdoor crops. Currently, this volatile compound is used in conjunction with sticky traps for monitoring thrips predominantly in greenhouses in Northern Europe. In the present study, in a nectarine [Prunus persica (L.) (Rosaceae)] orchard and an outdoor capsicum [Capsicum annuum L. (Solanaceae)] crop in Spain, blue sticky and white water traps with MI caught significantly more WFT than traps without MI. The volatile compound also significantly increased both blue sticky and white water trap capture of anthocorids – predominantly Orius laevigatus (Fieber) (Hemiptera: Anthocoridae) – in the capsicum crop. These results indicate that the behaviour of both WFT and O. laevigatus were altered by the presence of the compound and suggest there is potential to develop novel tools based on MI in conjunction with biological control strategies for thrips management.     

Intraguild predation among plant pests: western flower thrips larvae feed on whitefly crawlers

Omnivores obtain resources from more than one trophic level, and choose their food based on quantity and quality of these resources. For example, omnivores may switch to feeding on plants when prey are scarce. Larvae of the western flower thrips Frankiniella occidentalis Pergande (Thysanoptera: Thripidae) are an example of omnivores that become predatory when the quality of their host plant is low. Western flower thrips larvae usually feed on leaf tissue and on plant pollen, but may also attack eggs of predatory mites, their natural enemies, and eggs of the two-spotted spider mite Tetranychus urticae Koch (Acari: Tetranychidae), one of their competitors. Here, we present evidence that western flower thrips larvae prey on Trialeurodes vaporariorum Westwood (Hemiptera: Aleyrodidae), another competitor for plant tissue. We tested this on two host plant species, cucumber (Cucumis sativa L.), considered a host plant of high quality for western flower thrips, and sweet pepper (Capsicum annuum L.), a relatively poor quality host. We found that western flower thrips killed and fed especially on whitefly crawlers and that the incidence of feeding did not depend on host-plant species. The developmental rate and oviposition rate of western flower thrips was higher on a diet of cucumber leaves with whitefly crawlers than on cucumber leaves without whitefly crawlers, suggesting that thrips do not just kill whiteflies to reduce competition, but utilize whitefly crawlers as food.     

Microsatellite evidence for obligate autogamy,but abundant genetic variation in the herbaceous monocarp Lobelia inflata (Campanulaceae)

Although high levels of self‐fertilization (>85%) are not uncommon in nature, organisms reproducing entirely through selfing are extremely rare. Predominant selfers are expected to have low genetic diversity because genetic variation is distributed among rather than within lineages and is readily lost through genetic drift. We examined genetic diversity at 22 microsatellite loci in 105 individuals from a population of the semelparous herb Lobelia inflata L. and found (i) no evidence of heterozygosity through outcrossing, yet (ii) high rates of genetic polymorphism (2–4 alleles per locus). Furthermore, this genetic variation among lineages was associated with phenotypic traits (e.g. flower colour, size at first flower). Coupled with previous work characterizing the fitness consequences of reproductive timing, our results suggest that temporal genotype‐by‐environment interaction may maintain genetic variation and, because genetic variation occurs only among lineages, this simple system offers a unique opportunity for future tests of this mechanism.     

Will phenotypic plasticity affecting flowering phenology keep pace with climate change?

Rising temperatures have begun to shift flowering time, but it is unclear whether phenotypic plasticity can accommodate projected temperature change for this century. Evaluating clines in phenological traits and the extent and variation in plasticity can provide key information on assessing risk of maladaptation and developing strategies to mitigate climate change. In this study, flower phenology was examined in 52 populations of big sagebrush (Artemisia tridentata) growing in three common gardens. Flowering date (anthesis) varied 91 days from late July to late November among gardens. Mixed‐effects modeling explained 79% of variation in flowering date, of which 46% could be assigned to plasticity and genetic variation in plasticity and 33% to genetics (conditional R² = 0.79, marginal R² = 0.33). Two environmental variables that explained the genetic variation were photoperiod and the onset of spring, the Julian date of accumulating degree‐days >5 °C reaching 100. The genetic variation was mapped for contemporary and future climates (decades 2060 and 2090), showing flower date change varies considerably across the landscape. Plasticity was estimated to accommodate, on average, a ±13‐day change in flowering date. However, the examination of genetic variation in plasticity suggests that the magnitude of plasticity could be affected by variation in the sensitivity to photoperiod and temperature. In a warmer common garden, lower‐latitude populations have greater plasticity (+16 days) compared to higher‐latitude populations (+10 days). Mapped climatypes of flowering date for contemporary and future climates illustrate the wide breadth of plasticity and large geographic overlap. Our research highlights the importance of integrating information on genetic variation, phenotypic plasticity and climatic niche modeling to evaluate plant responses and elucidate vulnerabilities to climate change.     

东亚小花蝽对西方花蓟马和二斑叶螨的捕食选择性

多食性天敌对猎物的捕食选择性及猎物密度对天敌捕食的干扰作用直接影响到天敌对不同猎物的控制作用.在实验室条件下研究了东亚小花蝽对西方花蓟马和/或二斑叶螨不同虫态的捕食选择性,以及两猎物中一种猎物的密度变化对小花蝽取食另一种猎物的影响.结果如下:东亚小花蝽5龄若虫和成虫对西方花蓟马2龄若虫的捕食选择性均强于对其成虫,对二斑叶螨的选择性为雌成螨>若螨>幼螨.实验中西方花蓟马2龄若虫是东亚小花蝽最喜好的虫态.二斑叶螨雌成螨密度固定为60头/19.63cm2,西方花蓟马若虫密度从10增加到60时显著地减少了东亚小花蝽对二斑叶螨的取食.反之,固定西方花蓟马同样密度,增加二斑叶螨密度却没有显著改变小花蝽对西方花蓟马的取食.此结果进一步表明,西方花蓟马是东亚小花蝽更喜好的猎物.     

Foraging behavior responses of Orius insidiosus to thrips cues

The minute pirate bugs (Hemiptera: Anthocoridae) are effective biological control agents against destructive agricultural pests such as the western flower thrips, Frankliniella occidentalis Pergande (Thysanoptera: Thripidae) in agroecosystems around the world. One species, Orius insidiosus (Say), has proven effective in controlling thrips populations in fields and greenhouses, and serves as an integral component of many integrated pest management (IPM) programs. Three experiments were conducted using motion-tracking software and dual-choice Y-tube bioassays to determine whether direct thrips contact and thrips cues contact induced arrestant and attractant behaviors. The experiments revealed that O. insidiosus adults exhibited behavioral changes indicative of switching from extensive to intensive foraging after direct exposure to thrips prey. Similar arresting behavior was induced by the presence of thrips tracks alone. In Y-tube bioassays O. insidiosus showed preference towards arms containing tracks from western flower thrips larvae vs. clean arms, but only when direct contact with the tracks was made in the stem. Our data indicate that thrips deposit non-volatile semiochemicals that are used by O. insidiosus during foraging. These compounds have the potential to aid in O. insidiosus behavior manipulation which may help in early control of thrips populations in fields and greenhouses. Further research is necessary to determine the chemical composition of these cues and how to effectively and pragmatically integrate the inducing stimuli into biocontrol programs as part of IPM strategies.     

入侵害虫西花蓟马及其他8种常见蓟马的分子鉴定

用PCR产物直接测序法对入侵害虫西花蓟马和其他8种蓟马的线粒体 COⅠ基因433 bp片段测序，获得62个个体的序列。分子数据分析显示： 种内个体间平均遗传距离在0～0.005之间，2003年在北京发现的西花蓟马与欧洲等地区报导的西花蓟马不存在明显的遗传差异； 9种蓟马种间平均遗传距离为0.213。构建的NJ树可以很好的显示蓟马的聚类，物种各单元型最初分支自展值均达到100%。结果表明，基于PCR及直接测序技术的分子鉴定可以达到准确鉴定蓟马物种之目的。     

Management of thrips (Thysanoptera: Thripidae) in Australian strawberry crops: within-plant distribution characteristics and action thresholds

Abstract  Management of thrips in a hydroponic strawberry crop near Sydney, New South Wales, was studied from 1999 to 2002. The main species present were western flower thrips, Frankliniella occidentalis (Pergande), plague thrips, Thrips imaginis Bagnall, and, occasionally, onion thrips, Thrips tabaci Lindeman. Their within- and between-plant distribution and the degree and type of damage caused are described, and used to recommend action thresholds. Flowers are identified as the primary monitoring site, and young green fruit as the key damage site. Action thresholds of approximately 45% of flowers with 5 or more adult western flower thrips, or 40% of flowers with 10 or more adult plague thrips are recommended. Alternative thresholds using all motile stages are given for flowers, and for young green and red berries. A higher tolerance is recommended during cool, wet periods.     

Oviposition preference of western flower thrips for cucumber leaves from different positions along the plant stem

While the distribution of herbivorous insects over leaves along the stem often shows a peak at some distance from the apex this does not necessarily reflect an innate preference as alternative explanations can be provided such as impact of predators and inter- or intraspecific competitors. It is of interest to determine which factors shape the distribution of insects over the leaves of a plant. Do leaves from different positions differ in suitability for insects and is that reflected in the insect's preference, or are other factors involved? In this paper we assess how the herbivorous insect western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), chooses among leaves from different positions relative to the apex of cucumber, Cucumis sativus (L.) plants. On leaf discs of a susceptible and three partially resistant cucumber accessions, thrips reproduction was highest on apical leaves and lowest on basal leaves. In dual-choice essays thrips females preferred younger leaves over older leaves for oviposition in all cucumber accessions tested, as was predicted from the no-choice assay. This indicates that differences in leaf suitability are an important factor in determining thrips distribution on cucumber plants.     

Isolation and characterization of six polymorphic microsatellite loci in the western flower thrips Frankliniella occidentalis (Insecta,Thysanoptera)

Highly polymorphic microsatellite markers can provide important demographic information on founder events and range expansion following initial introduction of invasive insect species. Six microsatellite loci were isolated from an enriched DNA library in order to study the invasion patterns of the western flower thrips, Frankliniella occidentalis. All loci tested were found to be polymorphic and successfully amplified in all individuals. The number of alleles per locus ranged from five to nine and heterozygosity ranged from 45 to 73%. Some of the loci were also successfully amplified in other thrips species.     

Management of western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), in hydroponic strawberry crops: using yellow sticky traps to determine action thresholds

Abstract  The relationship between western flower thrips (WFT) populations in flowers and catches on yellow sticky traps was investigated in a hydroponic strawberry crop in the Sydney area in 1999–2000. The thrips population was initially dominated by males, but by mid-summer it was composed primarily of females. At a point when approximately 60–65% of WFT on traps were female (approximately 20–30 females per trap), the overall density of thrips on traps and in the crop increased rapidly, resulting in severe damage to immature fruit. The sex ratio of 0.60–0.65 females corresponded very closely to a mean of five adult WFT per flower at the start of the trapping week, which was an infestation level previously calculated as the action threshold to prevent damage to young green fruit.     

西花蓟马的抗药性及其治理策略

西花蓟马Frankliniella occidentalis（Pergande）是世界性的园艺作物上的重要害虫,几乎对每种类型的杀虫剂均产生了抗药性,包括有机磷、氨基甲酸酯、拟除虫菊酯类杀虫剂和多杀菌素等。本文对国外西花蓟马的抗药性发展现状和抗性机制进行了总结,并提出了抗性治理策略,即科学合理使用杀虫剂,结合栽培防治、物理防治、生物防治和寄主植物抗性等方式降低杀虫剂对西花蓟马的选择压,从而达到抗性治理的目的。